# ./orc.txt中记录就是那一长段源代码中注释内容
with open('./orc.txt', 'r') as ff:
    content = ff.read()
# print(content)
from collections import Counter
counter = Counter(content)
ans = ""
counter = sorted(counter.items(), key=lambda x:x[1]) # 可删去排序
# print(counter)  # type: list
for key, times in counter:
    if times < 10: ans += key
print(ans)   # equality